The present invention relates to an automatic image-density control system, more particularly, to an automatic image-density control system for application to an electro-photographic copying machine which is provided with pre-scan format automatic image-density control function and continuous page copying function.
Conventionally, there are a wide variety of modern electrophotographic copying machines incorporating pre-scan format automatic image-density control function and continuous page copying function, while these respectively offer substantial advantages for allowing users to easily obtain high quality copies corresponding to the content of objective book page originals.
When continuously executing photo-copying of page-to-page content using any of conventional electrophotographic copying machines available today, control means first pre-scans the content of the first page and then samples data generated by the pre-scan operation before determining an optimum image density. Then, control means establishes the amount of exposure or development bias in order that the predetermined optimum image density can be achieved. The copying system then executes photographic copying of the first page content, and then by applying the exposure amount and development bias identical to those which were applied to the electrophotographic copying of the first page content, the copying system executes the electrophotographic copying of the content of the second page on.
Nevertheless, any of these conventional copying machines still has a critical problem to be solved. Despite a certain difference present in the kind and density of pictures between the first and second pages, any of these conventional copying machines is obliged to abide by the identical copying requirements for copying the content of the second page by applying the identical exposure or development bias which were applied to the copying of the first page content. More particularly, if the first page contains linear drawings and the second page neutral picture like a photograph, optimum amount of exposure or development bias applicable to linear drawing and optimum requirements applicable to the neutral picture significantly differ from each other. As a result, if a specific amount of exposure and a specific development bias suited for a certain picture were applied to a different picture, it merely results in the reproduction of a noticeably poor-quality picture, and yet, the reproduced picture may not easily be identified in an extreme case. If this occurs, operator is obliged to again execute copying of the content of the page that has turned out the faulty picture.
Although this problem can be solved by applying pre-scan operation immediately before starting with copying operations of the needed pages, it in turn generates another problem of lowering the copying speed due to extended duration for implementing pre-scan operation in conjunction with the total time needed for executing the designated copying operation.